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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Rebuilding a YS91
11-11-2005 10:46 PM  14 years ago
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dgshaffer

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New Jersey

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Rebuilding a YS91
As a winter project I'd like to rebuild my YS91. With so much talk of poor bearings installed from the factory, this is my goal. Here are my questions:

Degree of difficulty

What special tools are required

What should be replaced while it's apart

Tips on what to look out for during the rebuild

Is it more cost effective to send it in for this and if so will they use ceramic bearings if requested

Any input would be appreciated as well as a source for parts other than the obvious Heliproz or Ricks.

Thanks,
Don
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11-11-2005 11:28 PM  14 years ago
Furious Predator

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Kitchener, Ontario, Canada

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just take your time and be careful, i made the mistake of rushing myself, cost me a $20 piston ring because i wasn't paying attention to how i was installing the cylinder in relation to the piston liner.
i just finished rebuilding my YS80, i ordered the Ring and front bearing from ricks, and i got a supposedly upgraded bearing which is supposed to last longer then the stock ones from Lenco, its about half way down the page.
http://www.rchelisplus.com/Lencomainpage.htm
i cant say how good they are or if they infact last longer, because to be honest, i dont know how many runs my origional bearing had, and i only finished installing this new one last week.

i noticed much improved compression with the new ring, i didn't replace the liner though, no need to, it is in mint cond.

incase you have never replaced a main bearing. strip the engine down so its only the case and the main bearing still together. i take a small hobby torch and heat up the area outside the bearing on the case. then pick it up (with leather gloves) and give it a gentle tap on a hard (preferably fire resistant) surface. the bearing just pops out.

incase you have never replaced a ring, they are extremely brittle, bend them no more then needed (i learned the hard way).

i also blow it all out with compressed air in the end, and soak all the new parts in after run oil just for good measure.

hope this helps any.
Shawn
Team Leisure-Tech
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11-11-2005 11:38 PM  14 years ago
pinoy

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Muncie, Indiana USA/Obando, Bulacan Philippines

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The only thing I did with my two YS 91 is replaced the front and back bearings. I 've been hearing some noises and getting some vibrations in my other 91 so actually tonight I'll be replacing the rear bearing in it. The bearing that I used or getting ready to use is the OS 91 bearing that I ordered from Rick's RC. As far as I know I didn't use any special tools to replace it. I just take the carb., pump, head, piston, sleeve, and crank off then place the engine case with the bearing still in it ofcourse inside the oven and heat it for maybe 5 mins. and the bearing should fall off the engine easily when you tap the case against a table. While still hot, drop the new bearing inside the case and it should sit easily, I use the crank shaft to push the bearing in to make sure that it is actually all the way in there. You should be able to assemble the rest of it back from there. I'm not an engine expert but this technique work well with me.
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11-11-2005 11:41 PM  14 years ago
dgshaffer

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New Jersey

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That was a great start. It doesn't sound all that difficult.

To get the connecting rod off of the crank shaft I think I need to slip out the liner to allow the piston to tilt. Is this correct?
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11-11-2005 11:49 PM  14 years ago
Furious Predator

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yeah, thats the easiest way, atleast thats how i did it, you may need a little heat to get the liner loose, after that you have enough side to side play to pop the arm off the crank.Shawn
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11-11-2005 11:50 PM  14 years ago
mdu6

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Montreal

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Yes,

On the YS91 you might need to heat the engine to get the sleeve out.

Which is a good first step anyhow because you need heat to remove the
2 bearings.
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11-11-2005 11:55 PM  14 years ago
dgshaffer

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New Jersey

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To get the new bearings to seat I'm thinking a night in the freezer?
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11-11-2005 11:56 PM  14 years ago
Furious Predator

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what for?that will make it tight for only when its in the freezer. but i suppose if you really want a loose and easy instal, put the bearing in the freezer, and heat the case, should fall right in. its a tight fit int eh first place when they are at the same temp, thats the whole purpose in heating the case to take out the bearing.Shawn
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11-12-2005 12:02 AM  14 years ago
Furious Predator

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Kitchener, Ontario, Canada

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just to add one thing. if you stick your bearing in the freezer to help shrink it, i would suggest maybe soaking the bearing in after run oil, or something similar to protect it against precipitation while its warming back up.Shawn
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11-12-2005 12:13 AM  14 years ago
dgshaffer

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New Jersey

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Yes, I was referring to the bearing. Good tip on the oil. That would help keep it cold while I was installing it as an added bonus.

I just thought that since it was a tight fit it being cold would help to get it in place without having to hit it with anything.

I was thinking about the ceramic bearings as another option. There seem to be a bunch here that have tried them with good results.

I'm looking for parts but not having much luck finding anything in stock.
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11-12-2005 12:17 AM  14 years ago
Furious Predator

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Kitchener, Ontario, Canada

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that is why pinoy said to instal the new bearing while the case is still hot from takin out the old one, then it will pop in as easy as the old one poped out.
i know people that are using ceramic bearings on the YS90, but i dont know how many flights they have been able to put on them.
Shawn
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11-12-2005 12:54 AM  14 years ago
dgshaffer

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New Jersey

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That makes sense. Remove and install all at once. Seems like the smart thing to do.

I was hoping more people using the ceramics would jump in. Thanks for your thoughts Vigor. You've been a lot of help. As soon as it starts getting really cold I'll jump into this adventure.
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11-12-2005 01:07 AM  14 years ago
Heli88

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Clarkston, MI

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FWIW...I used ceramic bearings in my OS 50. They don't seem to last any more or less than stock bearings.
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11-12-2005 03:25 AM  14 years ago
rdalcanto

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Salt Lake City, UT

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If you replace the gaskets, the one under the carb has a little hole on one side that matches up with a little hole on the black plastic the carb sits on. Fuel comes up through there. If you have the gasket flipped 180 degrees, the fuel can't get through and the motor will not start. Don't ask me how I know....

Rick
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11-12-2005 03:28 AM  14 years ago
dgshaffer

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New Jersey

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Good note. I was planning on replacing the diaphram and gaskets while I had it apart. I'll keep an eye out for that little hole and which location it came from.

Does anyone know who stocks all of the parts I'll need?
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11-12-2005 04:51 AM  14 years ago
Ace Dude

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USA

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Don, I purchased a copy of this book a while ago and I find it very helpful. It's certainly worth the money. It has some good info. on rebuilding.

http://www2.towerhobbies.com/cgi-bi...p?&I=LXZ850&P=7
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11-12-2005 07:42 AM  14 years ago
crowfly

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Pleasant View, TN U.S.A.

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Take note of the fact that the cylinder liner is "clocked" or located in the block by a tiny roll pin driven into the deck of the block. The roll pin fits into a corresponding notch in the deck flange of the liner. Also when reinstalling the piston/rod combo. you will have two choices as to its orientation. Only one way is correct. The piston ring end gap is located on the piston by a pin that is driven in from the crown that intersects the ring grove. This prevents the ring from rotating. When it is oriented correctly the ring end gap will not pass through a port as the piston travels up & down. If you rotate the piston 180°, the ring end gap will pass through the exhaust port. Brrrrr, not good. When everything is oriented correctly, and viewing the engine while looking straight down into the cylinder, and the back plate facing towards you, The ring locater pin will be at approx. 8 o'clock. The liner locater pin will be at approx. 10 o'clock. Go slow, have fun, don't force it.

ps I use "mobil 1 mx2t " synthetic 2cycle motorcycle oil as assembly lube. Do not set it up "dry".
If God had meant for man to fly, he would have given him more money
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11-12-2005 10:22 AM  14 years ago
dgshaffer

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New Jersey

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Now we're getting into the details. This is good information. I'm sure that I'm not going to be the only one that gets something out of this thread. I'll bet there are a lot of guys that wish they could rebuild theirs but were affraid to dive in.

Thanks for the link to the book Pete. Where ya been? Sunday I'm heading to Jefferson to fly with a new friend. We need to hook up and fly!
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11-12-2005 03:22 PM  14 years ago
mdu6

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Montreal

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I personnally do not like to put the bearings in the freezer.

I find the cold/heat difference being so high, that any alignment problem
when you are seating the bearing can cause the bearing to realy stick on the casing. This makes it harder to re-align.

Also, I am not sure of the impact of the humidity/water that gets moved around when the cold/hot parts meet.

this is just an opinion, nothing scientific !
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11-12-2005 05:43 PM  14 years ago
dgshaffer

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New Jersey

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I guess that was a dumb idea. Just that I've had to use dry ice to remove huge flywheels off of equipment shafts. Old habits and all that!
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